Drum transfer apparatus

ABSTRACT

A frame is provided with at least two axially parallel cylindrical rollers on which a drum can be supported on its axially spaced wheels. The drum has axially projecting central pins, and a servicing arrangement is adjacent the frame so that the drum may be moved into the servicing arrangement and back to the frame, for servicing and operating purposes. The servicing arrangement has a guide surface extending from the region of the cylindrical rollers outwardly of the frame and having a free edge remote from the rollers. Two or more support elements are provided having edge faces provided with notches into which the axially projecting pins of the drum can engage when the drum rolls on its wheels over the guide surface and off the free edge.

United States Patent 1 Dreher DRUM TRANSFER APPARATUS Manfrid Dreher, Salmbach, Germany Dr.-Ing. Manfrid Dreher KG, Engelsbrand, Germany Filed: Sept. 1, 1971 Appl. No.: 176,854

Inventor:

[73] Assignee:

[30] Foreign Application Priority Data Sept. 2, 1970 Jan. 30, 197 1 Germany ..P 20 43 573.8 Germany ..P 21 04 418.8

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 1,097,852 9/1955 Germany ..51/l64 841,447 7/1960 GreatBritain ..5l/164 [4511' Apr. 10, 1973 383,194 10/1964 Switzerland ..5 H164 Primary Examiner-Harold D. Whitehead Assistant Examiner-Nicholas P. Godici Attorney-Michael S. Striker ABSTRACT A frame is provided with at least two axially parallel cylindrical rollers on which a drum can be supported on its axially spaced wheels. The drum has axially projecting central pins, and a servicing arrangement is adjacent the frame so that the drum may be moved into the servicing arrangement and back to the frame, for servicing and operating purposes. The servicing arrangement has a guide surface extending from the region of the cylindrical rollers outwardly of the frame and having a free edge remote from the rollers. Two or more support elements are provided having edge faces provided with notches into which the axially projecting pins of the drum can engage when the drum rolls on its wheels over the guide surface and off the free edge.

16 Clains, 4 Drawing Figures 1 PATENTED 3.726046 sum 1 UF 3 I Wen/0r.- mummy on E0!!- PATENTEDAFR 1 [H975 3 7'26 046 SHEET 3 BF 3 Fig.3

Fig. 4

DRUM TRANSFER APPARATUS CROSS-REFERENCE TO RELATED APPLICATION A related application was filed in my name on April 23, [971 under the title TRANSFER APPARATUS; it is copending under Ser. No. 136,844.

BACKGROUND OF THE INVENTION The present invention relates generally to a drum transfer apparatus, and more particularly to an apparatus in which one or more drums are normally supported on their axially spaced wheels on two or more axially parallel cylindrical rollers, which drums can be moved to a servicing arrangement and from the same back to the support arrangement.

It is already known to provide an apparatus of the general type here in question having a frame provided with several pairs of cylindrical rollers, with the pairs being located at different levels one above the other. The wheels of drums which are to be used in conjunc tion with this apparatus, and which wheels are provided in the region of the opposite axial ends of the drums, contact the peripheries of the rollers of the respective pairs and, when one or both of the rollers of each pair is driven, the drum is rotated. When the drum is charged in its interior with materials or objects which are to be processed, for instance which are to be polished or abraded, the rotation of the drum will effect the desired processing, for which purpose it may of course be necessary not only to introduce the articles to be processed but also a suitable processing material, such as a polishing paste or the like.

The frame of this prior-art apparatus provides for each group of horizontal drums a servicing arrangement which can be shifted longitudinally of the frame so as to be placed in a position in which it can operate with a selected one of the drums, that is whichever drum is to be removed from the frame for discharging and/or charging purposes. The servicing arrangement then receives the selected drum which is so supported by it that it can be turned about its longitudinal axis to a position in which the charging and discharging opening of the drum which can be closed with a suitable closure can be directed downwardly for discharging purposes, and subsequently can be directed upwardly for charging purposes. When a drum is to be removed from the frame of the apparatus, it is first made to roll with its wheels onto a plate or onto transverse rails provided for this purpose, and then axially extending projections or pins at its opposite axial ends roll onto an upwardly inclined guide rail, with the drum being manually advanced in this rolling mode until the pins move into engagement'withan arresting device located at such a level that once the pins are arrested the drum is freely turnable and its wheels are out of engagement with whatever surface they previously contacted. Now the drum can be opened and turned so that its opening faces downwardly so that the contents are discharged by gravity. Thereupon the drum can be charged again after first turning it so that its opening faces upwardly, and after the arresting device is released the drum is rolled back onto the frame until its wheels again rest on the pair of rollers which then move it in rotation.

This known prior-art apparatus has been found to be quite effective for its intended purposes. It has, however, similarly been found that this apparatus provides difficulties under certain circumstances, namely that when the drums are more or less filled and correspondingly heavy, relatively substantial effort is required on the part of an operator to roll them manually up the inclined guide rails until their axial pins engage and cooperate with the arresting devices.

, Furthermore it has been found that the priorart apparatus cannot be readily used with drums of different dimensions and with correspondingly different wheel diameters because drums having a large volumetric capacity and a correspondingly large diameter of their wheels must be moved along the guide rails to a relatively high position before their wheels are out of engagement with the surface on which they have previously rolled during their movement from the cylindrical rollers to the arresting device.

A further proposal known from the prior art suggests to so construct the servicing arrangement that the wheels of the drums willwhen the drums are rolled off the associated cylindrical ro1lers--move onto short guide rails which are declined, that is which are inclined in a downward direction. The purpose is that the drum should be moved downwardly once its guide wheels engage these guide rails, and the wheels are then to contact supporting rollers on which the drum is to be turnable to a discharging and subsequently to a charging position. Although this arrangement is suitable for drums and wheels of different dimensions, the turning of the drum when the latter is supported with its wheels on supporting rollers, and the restoration of the drum up the inclined guide rails and onto the cylindrical supporting rollers, require relatively significant forces also be exerted by the operator, and this construction therefore is subject to the same objections raised above with respect to the first-mentioned priorart construction in terms of the energy and effort to be expended by an operator.

SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to overcome the disadvantages of the prior art. More particularly it is an object, of the present invention to provide an apparatus of the type here under discussion in which the servicing means is so improved that the movement of drums to and from the servicing means can be accomplished readily and without requiring the exertion of significant effort on the part of an operator.

At the same time it is an object of the present invention to provide such a construction which is relatively simple and uncomplicated.

In pursuance of the above objects, and of others which will become apparent hereafter, one feature of the invention resides, in an apparatus of the type here under discussion, in a combination comprising at least one drum having a circumferential wall, support wheels at opposite axial ends of the drum and projecting radially beyond this wall, and axially projecting pins at the opposite axial ends of the drum. Support means are provided, being adapted to receive the drum for rotatably supporting the same on the support wheels thereof, and servicing means are located adjacent the support means for rollingly receiving the drum from and returning it to the support means. According to the invention the servicing means comprises a guide surface for the support wheels of the drum extending away from the support means and having a free edge remote from the latter. At least two support elements are provided which project at least in part upwardly of the guide surface in the region of the opposite axial ends of the drum, and at least one recess is provided on each of the support elements at a side of the free edge which is remote from the support means and with the recesses being located at such a level that the respective pins will enter into the recesses when the support wheels roll off the guide surface beyond the free edge thereof.

With such a construction the drum need originally be rolled only in a substantially horizontal path after it has become disengaged from its associated cylindrical supporting rollers, and then it will move downwardly by a small distance under its own weight, until its pins engage in and become seated in the respective recesses.

In a currently preferred embodiment of my invention the recesses are so arranged and configurated that the arcuate path traversed by the pins of the drum after the drum support wheels roll off the free edge of the guide surface, is so large that when the pins are received in the recesses the periphery of the drum wheels will be located at a small distance from the free edge. This means that when the pins subsequently become disengaged from the recesses, that is when the drum is to be returned to the support means, the wheels of the drum will immediately contact the free edge of the guide surface and will immediately thereafter rest on the guide surface along which the drum can then roll.

Furthermore, it is advantageous that the construction be such that when during return movement of the drum from the servicing means to the support means the pins are lifted over the edges bounding the respective recesses, the peripheries of the respective drum support wheels will be located immediately adjacent the free edge, or contact the latter in such a manner that the free edge extends tangentially to the periphery of the drum support wheels. This arrangement of the recesses with respect to the dimensions of the drum support wheels is particularly suitable in a construction in which several pairs of recesses are provided, with the recesses of each pair being adapted for engagement with the pins at the opposite axial ends of the drum. The pairs of recesses may then be spaced from one another at a specific distance which can have a relationship to the diameters of the drum support wheels. In order to reduce to a minimum the distance by which the drum must be subsequently raised to disengage the pins from the respective recesses, it is advantageous if the height at which the pairs of recesses are located above the guide surface increases with their distance from the free edge of the guide surface.

According to a further embodiment of the invention, drums having a relatively large volumetric content and correspondingly large-dimensioned support wheels, can manually be disengaged with their pins from the respective recesses in a particularly simple and advantageous manner, and be returned to support on the cylindrical support rollers of the support means, when the difference in the spacing of their pins from the guide surface while the wheels rest on the latter, to the distance of the pins from the guide surface when the wheels have rolled off the free edge of the guide surface (that is when the pins are received in the respective recesses) correspond to the depth necessary for full entry of the pins into the associated recesses. With such an arrangement it is assured that filled and correspondingly heavy drums can be disengaged from the recesses of the servicing means without requiring significant manual exertion, simply by exerting a momentary force upon one or both of the support wheels of a drum whose pins are received in the associated recesses, whereby the pins become disengaged from the recesses and the drum will begin to move back to the support means.

Particularly if the servicing means is to be capable of accommodating drums of different dimensions, then it is advantageous in accordance with a further embodiment to provide lateral support elements on the servicing means having upwardly directed edge faces in which the different pairs of recesses are provided, with the recess in each edge face being spaced at different distances from the free edge of the guide surface. At least two such recesses should then be provided in each other edge face, and it is particularly advantageous if the construction is such that regardless of the size of drum accommodated in the servicing means, the distance between the circumferential wall of the drum and the bottom wall of the servicing means will always be at least substantially the same, because this makes it possible to use always the same receptacle for discharging the contents of differently dimensioned drums. To make this possible the invention contemplates to have the upwardly directed edges provided with the recesses rise in direction away from the support means and the free edge, in such a manner that the end portion of the respective upwardly directed edge face closer to the free edge will be spaced upwardly from the guide surface by a distance which is smaller than the radius of the wheels of the smallest of the drums to be used, whereas the end portion remote from the free edge will be spaced upwardly from the guide surface by a distance which is greater than the radius of the wheels of the smallest drum. In this manner the pins of the drums will initially contact the upwardly directed edge faces before reaching the recesses, will roll upwardly along these edge faces and will contact the first set of recesses only after the wheels of the respective drum are out of engagement with the guide surface.

To assure in such a construction that drums of different size will be reliably retained in the respectively associated recesses, even when the drum has significant momentum on entry of the pins into the respectively associated recesses, it is advantageous to so configurate the recesses that they would have a lesser height at the side facing towards the free edge and a greater height at the side facing away from the free edge. The lesser height advantageously will be so selected that it corresponds to a fraction of the diameter of the pins.

Of course, when the contents of a drum which has been moved into the servicing means are to be discharged, they must be intercepted and collected. It is therefore particularly advantageous according to a further embodiment of the invention to provide a receptacle beneath the region of the servicing means where the drums will be retained when their pins engage in the respective recesses, which receptacle may be connected with a mounting rail with the aid of which a longitudinal movement of the servicing means lengthwise of the support means can be produced. The

mounting rail can advantageously be configurated as a conduit or trough communicating with the receptacle and receiving for instance treating liquid or the like which issues from the drum when the latter is opened, and which is then conducted away from the receptacle via the hollw mounting rail. The latter may be connected with guide rails extending longitudinally of the support means so as to be capable of performing the desired movement in longitudinal direction of the support means.

The support means itself may have any desired number of superimposed levels, each of which in turn may have means for accommodating one or several drums in the manner disclosed in my aforementioned copending application, and in such an event it is advantageous to provide each level with the servicing means according to the present invention.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partially sectioned side view taken along line I-I of FIG. 2 showing a drum accommodated in the servicing means;

FIG. 2 is a top-plan view of FIG. 1 but showing the drum accommodated in the support means rather than in the servicing means;

FIG. 3 is a somewhat diagrammatic view analogous to FIG. 1, but illustrating a further embodiment of the invention and showing diagrammatically a drum having large-dimensioned wheels; and

FIG. 4 is a view similar to FIG. 3 but showing in the same embodiment a drum having smaller-dimensioned wheels.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing the drawing in detail, and firstly the embodiment illustrated in FIGS. 1 and 2, it will be seen that reference numeral 1 identities in toto a support means or frame of an apparatus according to the present invention. The support means has in the illustrated embodiment four upright corner supports 12 and a number of transverse braces or supports 14. In the middle 1 of the transverse braces 14 there are journalled in a manner known per se and therefore not illustrated in detail, two axially parallel cylindrical rollers 16 for turning movement; one of these rollers 16 is driven, also in a manner known per se and which does not form a part of the present invention.

In FIG. 1 [have illustrated in broken lines a drum 18 supported on the rollers 16, the drum having a circumferential wall 22 which defines a hollow interior, provided at its opposite axial ends with two support wheels which rest with their peripheries on the rollers 16, and axially projecting pins 24. It will be appreciated that when one of the rollers 16 is driven in rotation, frictional motion transmission will take place to the wheels 20 of the drum 18, whereby the latter is rotated and in turn also rotates the non-driven roller 16. The contents of the hollow interior of the drum 18 will thus become agitated with the desired effect which latter, however, is not of any consequence for the purposes or an understanding of the present invention.

Reference numeral 30 identifies in toto a servicing arrangement according to the present invention which in the illustrated embodiment is provided with two transversely spaced plate-shaped support elements 32 and 34 (compare FIG. 2). These elements 32 and 34 are rigidly connected with one another by braces of which a brace 36 and a guide plate having an upper supporting or guide surface 38 are clearly shown in FIGS. 1 and 2. It is also possible and illustrated-but not necessary-4o provide a bottom plate or wall 40 connecting the support elements 32 and 34, with a receptacle 50 being located above the bottom wall 40 and provided in turn in its own bottom with a screen 52. The upwardly directed edge faces 42 and 44 of the elements 32 and 34, respectively, are each provided with a first recess 46 and a second recess 48 which are respectively closer to and farther :spaced from the free edge 72 of the guide surface 38.

The arrangement 30 is further provided on the side facing the frame 10 with two longitudinally spaced mounting rails 54 at least one of which is configurated as a hollow conduit or trough (compare FIG. 1) and provided with an outlet opening 56 which is located above and communicates with a trough 58 extending in parallelism with the rollers 16 and inclined in one or the other axial direction of the rollers 16. A pair of guide rails 68 and are provided on the frame 10, being closed except for a downwardly directed guide slot through which arms 60 and 62 provided on the mounting rails 54 extend, which arms carry in the interior of the rails 68 and 70 respective pairs of rollers 64 and 66.

In operation of the embodiment in FIGS. 1 and 2, and assuming that a drum 18 is accommodated in the frame 10 on a pair of rollers 16 and. is to be removed for inspection of its contents or for discharging of its contents, or for another reason, the arrangement 30 is moved longitudinally of the rollers 16 by shifting it along the rails 68 and 70. Such shifting is continued until the arrangement 30 is juxtaposed with the roller 18 which it is to receive, that is until it assumes a position such as illustrated in FIG. 2. Of course, if only a single drum 18 is accommodated on the rollers 16, then the arrangement 30 could conceivably also be made stationary rather than movable.

In any case, the drum 18 is rolled off the rollers 16, that is from the chain-line position shown in FIG. 1 until its wheels 20 are supported on the guide surface 38. On this guide surface 38 the wheels roll along until they reach the free edge 72, where they are now no longer guided. In the absence of further guidance the drum drops slightly once the wheels 20 move beyond the free edge 72, and its pins 24 engage in a pair of the recesses provided in the elements 32, 34, that is either in the recesses 46 or in the recesses 48. In the illustrated embodiment the engagement takes place with the recesses 48, being determined by the diameter of the wheels 20 on the drum 18. The distance from the free edge 72 to the recesses 48 is so selected that the pins 24 will enter into these recesses 48 without requiring any specific action on the part of an operator. For this reason it is advantageous when this distance corresponds approximately to the radius of the wheels 20.

Once the drum 18 is in this position, which is shown in full lines in FIG. 1, it can be readily turned because it is journalled on the pins 24so that its opening (not illustrated) is directed downwardly whereby, when the opening is uncovered, the contents of the drum will be discharged from the latter under the influence of gravity. The contents will then enter into the receptacle S and be collected therein, whereas any liquid or particles of small enough size will pass through the screen 52 and flow along the bottom wall 40 into the single or several hollow mounting rails 54, to leave the latter through the opening 56 and to enter into the trough 58 for further conveyance. Subsequently the drum is turned until its opening faces upwardly, whereupon it can be filled again and the opening closed. Then the drum is again rotated until it is returned to the chainline position illustrated in FIG. 1 for further operation.

In FIGS. 3 and 4 I have illustrated an embodiment in which only the servicing arrangement 130 is shown, the frame and the rollers having been omitted as not essential for an understanding of the invention, it being understood that they can be of the same type and construction shown in FIGS. 1 and 2.

In the embodiment in FIGS. 3 and 4 the support elements 32 and 34 are replaced with the support elements 132 which constitute part of a supporting arrangement 134 beneath which the servicing arrangement is provided with a bottom plate 140 which is downwardly inclined towards the left, that is towards the frame which will be located to the left of the arrangement 130.

The two support elements 132, of which only one is visible, each are provided with an upwardly inclined upper edge face 142, which again may each be provided with two recesses 146 and 148, with the recess 148 being located farther from the free edge 176 of the guide surface 172 than the recess 146. The device 134 forms a receptacle above the bottom wall 140, with the bottom of the receptacle being constituted by a screen 152. The plate member having the guide surface 172 is provided with lateral upwardly extending wall portions 174.

As FIGS. 3 and 4 clearly show, the recesses 148 (only one shown) are intended for cooperating with the axial pins 124 of a drum 1 18 having large-dimensioned wheels as opposed to another drum having smallerdimensioned wheels with whose axial pins the recesses 146 (one shown) are intended to cooperate. Recesses 148 are so provided on the elements 132 that the difference in the distance a of the pins 124 ofa drum 118 above the guide surface 172 before the wheels 120 roll off the free edge 176, to the distance b which the pins 124 assume above the guide surface 172 after the pins are received in the recesses 148, corresponds to a depth 0 which is necessary for a proper entry of the pins 124 into the associated recesses 148. With such a construction I assure that a filled and correspondingly heavy drum can be disengaged manually without requiring any significant bodily exertion from the recesses 148, and can be returned to the guide surface 172 and from there to the non-illustrated drive rollers (corresponding to the rollers 16 of FIGS. 1 and 2).

Furthermore, in this embodiment the just described location of the recesses 148 assures that when the pins are received in the recesses 148, the circumference of the wheels of the drum 118 will be spaced only by a small distance from the free edge 176, with the surface 172 extending tangentially to this circumference, whereby immediately after disengagement of the pins from the recesses 148 the wheels will again contact the surface 172, thereby avoiding the necessity for the exertion of additional manual force to lift the wheels over the free edge 176 and onto the surface 172 upon disengagement of the pins from the recesses 148.

The recesses 146 are provided, as already indicated above, for cooperation with the axial pins of a drum having a smaller volumetric content drum 182, having correspondingly smaller-dimensioned wheels. The position of the recesses 146 is so selected that the circumferential wall of the drum 182 when the pins thereof are received in the recesses 146, will be spaced from the screen 152 essentially by the distance as the circumferential wall of the drum 118 when the pins of the latter are received in the recesses 148. This means that despite the differential dimensions of the two drums one and the same receptacle can be used during discharging of the contents of the drums, which receptacle 180 will be placed between the elements 132 and deposited on the screen 152.

In order to assure that in the position in which their pins are received in the recesses 146 the smallerdimensioned drums 188 will be located at the same height as the larger drums 118, the construction is such (compare FIG. 4) that the smaller drum 188 must first be upwardly raised before its pins 184 can be received in the recesses 146. For this purpose the height of the upper edge faces 152 at the ends portions thereof closer to the surface 172 and above the surface 172, is smaller than the radius of the wheels 186 of the drum 182, whereas at the opposite end portion the height above the surface 172 is greater than the radius of the wheels 186. This means that when the smaller drum 188 is moved from the left towards the right in FIG. 4, its pins ,184 will initially contact the upper edge faces 142 and roll upwardly along the same, lifting the drum 188, until they enter into the recesses 146. In this position the drum 188 will be maintained in such a location that the distance of its circumferential wall 183 from the screen 152 is substantially the same as the distance d of the circumferential wall 122 of a larger drum 118 whose pins are received in the recesses 148.

It should be noted in FIGS. 3 and 4 that the contour of the edge bounding the recesses 148 at the end 188 facing towards the free edge 176 is so configurated that it corresponds approximately to the are which the pins 124 of the larger drum 118 will traverse when the wheels 120 of this drum roll off the free edge 176. Furthermore, the height of the recesses 146 and 148 at the side facing towards the free edge 176 is lower than their height at the opposite side, thereby assuring that if the drum is rolling along towards entry into the respective recesses with substantial velocity, the pins cannot first enter into the respective recesses and then jump out of them and the drum fall out of the servicing arrangement.

It will be understood that each of the elements described above, or two or more together may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a drum transfer apparatus, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the appended claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. In an apparatus as described, in combination, at least one drum having a circumferential wall, support wheels at opposite axial ends of said drum and projecting radially beyond said wall, and axially projecting pins at said opposite axial ends; support means adapted to receive said drum for rotatably supporting the same on said support wheels thereof; and servicing means adjacent said support means for rollingly receiving said drum from and returning it to said support means, said servicing means comprising a guide surface for said support wheels extending away from said support means and having a free edge remote from the latter, at least two support elements projecting at least in part upwardly of said guide surface in the region of said opposite axial ends, and at least one recess on each of said support elements at a side of said free edge which is remote from said support means and located at such a level that the respective pins will enter into said recesses when said support wheels roll off said guide surface beyond said free edge.

2. In an apparatus as defined in claim 1, wherein said guide surface is at least substantially horizontal.

3. In an apparatus as defined in claim 1, said pins being coaxial with one another and with said wheels, and wherein said wheels each have a predetermined radius, and wherein the distance of said recesses from said free edge is slightly greater than said predetermined radius.

4. In an apparatus as defined in claim 1, each of said recesses being bounded by an edge portion having, at a side closer to said free edge, a concavely arcurate contour.

5. In an apparatus as defined in claim 1, each of said recesses being bounded by an edge portion having, at a side closer to said free edge, a contour so selected that on movement of said pins into and out of said recesses in contact with said edge portion, said wheels are immediately proximal to said free edge and said guide surface is tangential to the periphery of said wheels.

6. In an apparatus as defined in claim 1, said servicing means further comprising at least one additional recess on each of said support elements and remote from said free edge by a distance which is different from that by which the respective one recess is remote therefrom.

7. In an apparatus as defined in claim 6, wherein said additional recess of each support element is located intermediate said free edge and said one recess, and at a level above said support surface which is lower than the level of said one recess.

8. In an apparatus as defined in claim 1, wherein said support elements have edge faces which are directed upwardly away from said guide surface, and wherein said recesses are provided in said edge faces.

9. In an apparatus as defined in claim 8, wherein said edge faces are inclined upwardly of said guide surface in direciton away from said support means and free edge.

10. In an apparatus as defined in claim 9, wherein said edge faces are substantially smooth except for said recesses provided therein.

11. In an apparatus as defined in claim 9, said pins being coaxial with one another and with said wheels, and said wheels having a predetermined radius; and wherein said edge faces each have a first end portion closer to said free edge and spaced upwardly of said guide surface by a distance smaller than said radius, and a second end portion farther from said free edge and spaced upwardly of said guide surface by a distance greater than said radius.

12. In an apparatus as defined in claim 9, said recesses each having a lower side closer to, and a higher side farther from said free edge.

13. In an apparatus as defined in claim 12, wherein the depth of said recesses at said lower side thereof is a fraction of the diameter of the respective pins.

14. In an apparatus as defined in claim 1, said servicing means further comprising wall means defining a receptacle downwardly spaced from said recess, and screen means accommodated in said receptacle.

15. In an apparatus as defined in claim 1, said support means comprising a pair of axially parallel cylindrical rollers at least one of which is driven in rotation; and wherein said servicing means comprises guide rails located beneath said rollers extending longitudinallythereof, at least one mounting rail extending in part underneath said guide rails, and connecting portions connecting said mounting rail with said guide rails movable longitudinally of the latter so as to enable deplacement of said servicing means axially of said rollers.

16. An apparatus as defined in claim 15, wherein said mounting rail is of hollow trough-shaped configuration; said servicing means further comprising wall means defining a receptacle downwardly spaced from said recesses, and said mounting rail communicating with said receptacles. 

1. In an apparatus as described, in combination, at least one drum having a circumferential wall, support wheels at opposite axial ends of said drum and projecting radially beyond said wall, and axially projecting pins at said opposite axial ends; support means adapted to receive said drum for rotatably supporting the same on said support wheels thereof; and servicing means adjacent said support means for rollingly receiving said drum from and returning it to said support means, said servicing means comprising a guide surface for said support wheels extending away from said support means and having a free edge remote from the latter, at least two support elements projecting at least in part upwardly of said guide surface in the region of said opposite axial ends, and at least one recess on each of said support elements at a side of said free edge which is remote from said support means and located at such a level that the respective pins will enter into said recesses when said support wheels roll off said guide surface beyond said free edge.
 2. In an apparatus as defined in claim 1, wherein said guide surface is at least substantially horizontal.
 3. In an apparatus as defined in claim 1, said pins being coaxial with one another and with said wheels, and wherein said wheels each have a predetermined radius, and wherein the distance of said recesses from said free edge is slightly greater than said predetermined radius.
 4. In an apparatus as defined in claim 1, each of said recesses being bounded by an edge portion having, at a side closer to said free edge, a concavely arcurate contour.
 5. In an apparatus as defined in claim 1, each of said recesses being bounded by an edge portion having, at a side closer to said free edge, a contour so selected that on movement of said pins into and out of said recesses in contact with said edge portion, said wheels are immediately proximal to said free edge and said guide surface is tangential to the periphery of said wheels.
 6. In an apparatus as defined in claim 1, said servicing means further comprising at least one additional recess on each of said support elements and remote from said free edge by a distance which is different from that by which the respective one recess is remote therefrom.
 7. In an apparatus as defined in claim 6, wherein said additional recess of each support element is located intermediate said free edge and said one recess, and at a level above said support surface which is lower than the level of said one recess.
 8. In an apparatus as defined in claim 1, wherein said support elements have edge faces which are directed upwardly away from said guide surface, and wherein said recesses are provided in said edge faces.
 9. In an apparatus as defined in claim 8, wherein said edge faceS are inclined upwardly of said guide surface in direciton away from said support means and free edge.
 10. In an apparatus as defined in claim 9, wherein said edge faces are substantially smooth except for said recesses provided therein.
 11. In an apparatus as defined in claim 9, said pins being coaxial with one another and with said wheels, and said wheels having a predetermined radius; and wherein said edge faces each have a first end portion closer to said free edge and spaced upwardly of said guide surface by a distance smaller than said radius, and a second end portion farther from said free edge and spaced upwardly of said guide surface by a distance greater than said radius.
 12. In an apparatus as defined in claim 9, said recesses each having a lower side closer to, and a higher side farther from said free edge.
 13. In an apparatus as defined in claim 12, wherein the depth of said recesses at said lower side thereof is a fraction of the diameter of the respective pins.
 14. In an apparatus as defined in claim 1, said servicing means further comprising wall means defining a receptacle downwardly spaced from said recess, and screen means accommodated in said receptacle.
 15. In an apparatus as defined in claim 1, said support means comprising a pair of axially parallel cylindrical rollers at least one of which is driven in rotation; and wherein said servicing means comprises guide rails located beneath said rollers extending longitudinally thereof, at least one mounting rail extending in part underneath said guide rails, and connecting portions connecting said mounting rail with said guide rails movable longitudinally of the latter so as to enable deplacement of said servicing means axially of said rollers.
 16. An apparatus as defined in claim 15, wherein said mounting rail is of hollow trough-shaped configuration; said servicing means further comprising wall means defining a receptacle downwardly spaced from said recesses, and said mounting rail communicating with said receptacles. 